I. Field of the Invention
The present invention relates to digital computers and, more particularly, to secondary data storage devices which are useful with digital computers.
A secondary storage device stores computer program code and or data even when the computer's power is turned off. Such behavior makes secondary storage devices so-called nonvolatile storage. Secondary storage devices usually also have a much larger data storage capacity than primary storage devices.
Primary storage devices are the computer's main memory, known as random access memory or RAM. Since the data they contain usually vanishes when the computer's power is turned off, primary storage is described as volatile storage.
Common secondary storage devices include magnetic hard disk drives. There are many different manufacturers of disk drives. For example, the IBM® Deskstar® series are popular magnetic hard disk drives sold as of this writing. See the IBM® Internet web site http://www.ibm.com/harddrive for more information. Seagate® Technology of Scotts Valley, Calif. makes the popular “U Series” line of magnetic disk drives. Seagate's phone number is 800-seagate, and their Internet web site is at http://www.seagate.com/products/discsales. Western Digital® Corporation of Lake Forrest, Calif. makes a popular line of magnetic hard disk drives called the “Caviar®” series. Western Digital's® phone number is 949-672-7000, and they have Internet web site at http://www.westerndigital.com/products/productcatalog.asp.
Common secondary storage device interfaces in use today include the IDE and SCSI interfaces. The Integrated Drive Electronics (IDE) interface comes in three types:
the IDE XT, the IDE AT (also known as the IDE ATA type interface) and IDE MCA type interfaces. The Enhanced Integrated Drive Electronics (EIDE) interface is often used for magnetic hard disk drives and CD ROM drives in home desktop personal computers. The SCSI secondary storage device interface is the Small Computer System Interface and comes in three types: the SCSI-1 interface, SCSI-2 and SCSI-3 type interfaces.
II. Prior Art
Available prior art devices include the Redundant Array of Inexpensive Disks (or RAID), the “Mobile Rack” which is a removable mounting rack for magnetic hard disk drives shown in U.S. Pat. Nos. 5,767,445 and 5,797,667, an external backup hard drive which can connect to the computer through a port or through a Universal Serial Bus (USB®) connection and a cable based hard drive mounting bracket backup kit. The concepts of RAID were extensively discussed and explained in an article published in 1988 by ACM at pages 106–116, authored by David A. Patterson, Garth Gibson and Randy H. Katz.
Although RAID devices can be configured in a MIRROR mode, the actual implementation generally requires skills beyond those of the average computer user. Many ways of using a RAID device require several magnetic hard drives but one configuration, known as a MIRROR, (also known as RAID MODE 1) requires only two. It is salient to note that the second drive has the same information as the first and is not merely a listing or compilation of the data on the first drive.
For example, if the mirrored drive is one from which the system can be started, sometimes know as a boot drive, then the mirrored drive which the RAID device creates is also usable as a boot drive. In this mode of usage, the RAID device maintains the data on the second hard drive as an identical configuration of the first.
RAID devices can also include those manufactured in the form of peripheral cards (PCMCIA cards), RAID motherboards, and external RAID devices. RAID peripheral cards are auxiliary products which are inserted into special machine ports, generally found on lap top devices. External RAID devices, which are stand alone units outside of the computer case, are connected to it via a cable of some kind. RAID motherboards have RAID circuitry embedded in them.
Both the RAID device configured in a mirror mode and the device of the present invention, hereinafter referred to as the “safety cartridge,” protect against failure of the secondary storage device, most likely a magnetic hard disk drive. In the preferred embodiment, the safety cartridge includes two, substantially identical magnetic disk drives and drive circuitry for simultaneous parallel operations on both disks. One of the disks may be considered the main memory and the other, the back up or check disk.